This font is called blackboard bold and can be typed using the \mathbb{} command. p.s. \mathbb actually refers to blackboard bold, which adds some specific lines to the original letters, so it is sometimes called double struck. Does anyone know a good resource (preferably pictures) that illustrates a conventional way to write the special sets symbols, i.e.
A Baddie Hub The Ultimate Guide
$\\bbb p$ i am familiar.
Young authors (and some older ones) seem to prefer blackboard bold to plain bold for the standard number systems (and/or they pick it up by osmosis on web sites such as this.
In the first post of the thread "cardinal number subtraction", cardinal number subtraction there is a symbol for some kind of set which looks like this:
